1. Field of the Invention
The present invention is directed to a differentiating circuit for asynchronous systems and, more particularly to a self-clocking, self-timing differentiating circuit for digital asynchronous systems which can be used alone as a differentiating circuit or in combination with other circuits to form AND, OR, etc. logical circuits having a differentiated signal output.
2. Description of the Prior Art
Boolean algebra is frequently used to specify the states entered by logical circuits by means of tables that indicate output values in connection with inputs for combinatorial networks, and also to specify inside states for sequential networks. The representation is a description of "steady" variables, as of the elements that perform the logical operations were ideal elements lacking any physical feature whatever. Of course, in actual circuit implementation the physical parameters that "deviate" from the ideal behavior of these circuits must also be considered. The usual methods for implementation of digital circuits takes into account such deviating parameters in a merely "statistical" manner, without considering the variables of interest during signal transitions, since under this circumstance they would assume values generally defined as arbitrary. To avoid effects of such arbitrary values a "clock" element is typically used which enables the circuit to settle for the necessary time in order that the transients caused by the various transit times, particularly of physical devices, may expire. In other words, the clock enables the operations to occur in orderly fashion by connecting the timing with only the stable circuit conditions evoked by Boolean algebra so that transient arbitrary values are not used.
It is also known that circuits which utilize signals from a logic circuit may use signals having transient variations. The concept of variation is, however, tied to the mathematical concept of the first derivative of the variable as compared with time.
The solution of the practical problem of utilization of the "time derivative" signal is achieved by circuits that are edge triggered. Edge triggered circuits have associated therewith a certain time which is likely sufficient so that circuits which use the meaning of the signal variation may utilize it as required. Thus, the derivative is built up by artiface using a local clock, the start of which of controlled by the variation of the variable and the stop of which is determined by a previously set time value. Naturally, the use of clock circuits to control the timing of various digital circuits introduces additional complexity and expense to the overall circuit design.